Semiconductor device including multi-layered interconnection and method of manufacturing the device

ABSTRACT

The semiconductor device includes a semiconductor substrate, and a multi-layer wiring portion including insulating layers and wiring layers alternately stacked one on another on a main surface of the semiconductor substrate. All of the wiring layers are made of a same basis metal, at least one of the wiring layers contains an additive element, and a concentration of the additive element is lower on an upper layer side than that on a lower layer side.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 10/778,180,filed Feb. 17, 2004 and is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2003-407888, filed Dec. 5,2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing the device, which can be applied to, for example, an LSI(large scale integrated circuit) involving multi-layeredinterconnection.

2. Description of the Related Art

Recently, the essential parts of computers or communication devices use,in most cases, an LSI circuit in which a great number of transistors andresistances are coupled with each other to form an electric circuitstructure and integrated on a chip. With this structure, the performanceof the entire device depends greatly on the performance of each singleunit of the LSI circuits used in the device. Therefore, the performanceof the LSI circuit can be improved by, for example, increasing thedegree of integration, that is, reducing the size of the elements thatconstitute the LSI circuit. In order to actually realize the reductionof size of these elements, it is necessary to reduce the size of thewiring section for connecting one element with another and to increasethe number of wiring layers.

However, at the same time, as a result of reducing the size of thewiring section and increasing the number of layers, that have beenadvanced in order to meet the demand of reducing the size of elements,the following drawback has become prominent. That is, the resistance ofthe conductive layer itself and the parasitic capacity between wiringsections (interwiring capacity, inter-layer capacity, etc.) areincreased, thereby causing more signal delay.

Under the circumstances, in order to reduce the parasitic capacitybetween the conductive layers, a method of decreasing the specificinductive capacity of an interlayer insulating film has been proposed.However, the reduction of the specific inductive capacity by this methodis limited due to the physical properties and the like of the material.

In the meantime, there has been proposal of a method of, for example,reducing the opposing area between conductive layers (or reducing thethickness of the wiring film) while lowering the specific inductivecapacity of the interlayer insulating film. However, with this method,the resistance value of the conductive layer is increased due to adecrease in the thickness of the film, although it is possible todecrease the parasitic capacity.

Under the circumstances, recently, the use of an aluminum (Al)-basedconductive layer, which is conventionally used, has been switched to theuse of a copper (Cu)-based conductive layer, Cu having a resistancevalue about 40% lower than that of Al, in order to reduce the wiringresistance. (See, for example, Jpn. Pat. Appln. KOKAI Publication No.H11-186273.)

However, the thickness of each conductive layer is significantly reduceddue to the increase in the number of conductive layers and the reductionin the size of layers, and therefore the current density, etc. of theconductive layer is increased. Thus, even with a Cu-based conductivelayer such as mentioned above, the lowering of the reliability isinevitable. Further, in the case of the Cu-based conductive layer, Cu inthe boundary between wiring layers, especially in a lower layer side, isdiffused, which results in the lowering of the reliability. Thus,switching from the Al-based conductive layer to the Cu-based conductivelayer makes it possible to reduce the wiring resistance; however at thesame time, the best method of lowering the interlayer capacity acts inreverse, and causes the lowering of the reliability of the conductivelayer.

BRIEF SUMMARY OF THE INVENTION

A semiconductor device according to an aspect the present inventioncomprises a semiconductor substrate, a multi-layer wiring portionincluding insulating layers and wiring layers alternately stacked one onanother on a main surface of the semiconductor substrate, all of thewiring layers being made of a same basis metal, at least one of thewiring layers containing an additive element, and a concentration of theadditive element being lower on an upper layer side than that on a lowerlayer side, the upper and lower layer sides are that of the multi-layerwiring portion, and an upper diffusion inhibiting layer formed on thetop of the lowest wiring layer, wherein a specific inductive capacity ofan insulating layer located on an upper side of an adjacent pair ofinsulating layers included in the multi-layer wiring portion is equal toor higher than that of an insulating layer located on a lower side ofthe adjacent pair, and the specific inductive capacity of the lowermostlayer is lower than that of the uppermost layer.

A semiconductor device according to a second aspect of the inventioncomprises a semiconductor substrate, a plurality of insulating layersstacked upon each other formed on the substrate, and a wiring layerformed in each of said insulating layers, each of the wiring layerscomprising a lower layer and a main conductor layer formed on said lowerlayer. A specific inductive capacity of an insulating layer located onan upper side of an adjacent pair of insulating layers included in amulti-layer wiring portion is equal to or higher than that of aninsulating layer located on a lower side of the adjacent pair, and thespecific inductive capacity of the lowermost layer is lower than that ofthe uppermost layer; each of the lower layers is formed of the samebasis metal; a concentration of an additive element in a lower layer ina lowermost one of said wiring layers is higher than a concentration ofthe additive element in a lower layer in an uppermost one of the wiringlayers; and an upper diffusion inhibiting layer formed on the top of thelowest wiring layer.

A semiconductor device according to a third aspect of the inventioncomprises a semiconductor substrate; a multi-layer wiring portionincluding insulating layers and wiring layers alternately stacked one onanother on a main surface of the semiconductor substrate, all of thewiring layers being made of a same basis metal, at least one of thewiring layers containing an additive element, and a concentration of theadditive element being lower on an upper layer side than that on a lowerlayer side, the upper and lower layer sides are that of the multi-layerwiring portion; and an upper diffusion inhibiting layer formed on thetop of the wiring layers, wherein a specific inductive capacity of aninsulating layer located on an upper side of an adjacent pair ofinsulating layers included in the multi-layer wiring portion is equal toor higher than that of an insulating layer located on a lower side ofthe adjacent pair, and the specific inductive capacity of the lowermostlayer is lower than that of the uppermost layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic structural diagram showing a cross section of asemiconductor device according to the first embodiment of the presentinvention;

FIG. 2 is a diagram showing a step in the process of a method ofmanufacturing the semiconductor device according to the firstembodiment;

FIG. 3 is a diagram showing another step in the process of a method ofmanufacturing the semiconductor device according to the firstembodiment;

FIG. 4 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the firstembodiment;

FIG. 5 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the firstembodiment;

FIG. 6 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the firstembodiment;

FIG. 7 is a diagram showing still another step in the process of amethod of manufacturing the semiconductor device according to the firstembodiment;

FIG. 8 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the firstembodiment;

FIG. 9 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the firstembodiment;

FIG. 10 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the firstembodiment;

FIG. 11 is a schematic structural diagram showing a cross section of asemiconductor device according to the second embodiment of the presentinvention;

FIG. 12 is a diagram showing a step in the process of a method ofmanufacturing the semiconductor device according to the secondembodiment;

FIG. 13 is a diagram showing another step in the process of a method ofmanufacturing the semiconductor device according to the secondembodiment;

FIG. 14 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to thesecond embodiment;

FIG. 15 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to thesecond embodiment;

FIG. 16 is a schematic structural diagram showing a cross section of asemiconductor device according to the third embodiment of the presentinvention;

FIG. 17 is a diagram showing a step in the process of a method ofmanufacturing the semiconductor device according to the thirdembodiment;

FIG. 18 is a diagram showing another step in the process of a method ofmanufacturing the semiconductor device according to the thirdembodiment; and

FIG. 19 is a diagram showing still another step in the process of amethod of manufacturing the semi-conductor device according to the thirdembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to accompanying drawings. In the explanations of theseembodiments, common structural parts are designated by the samereference numerals throughout the figures.

First Embodiment

With reference to FIGS. 1 to 10, a semiconductor device according to thefirst embodiment of the present invention and a method of manufacturingthe device will now be described. FIG. 1 is a schematic structuraldiagram showing a cross section of the semiconductor device according tothe first embodiment, taking, as an example, a case where four wiringlayers are formed on the main surface of a semiconductor substrate 11.

As shown in FIG. 1, a MOSFET (metal oxide semiconductor field effecttransistor) 13 is formed in an element formation region that isseparated by an element insulating film 12 embedded in the main surfaceof the semiconductor substrate 11. The MOSFET 13 includes a gate oxidefilm 15 formed on the semi-conductor substrate 11, a gate electrode 14formed on the gate oxide film 15 and an impurity diffusion region 16formed to be isolated in the semiconductor substrate 11 and serving assource-drain regions. Further, on the entire main surface of thesemiconductor substrate 11, an interlayer insulating film 17 is formed.

A multi-layer wiring portion including four wiring layers is formed onthe interlayer insulating film 17. The first to fourth wiring layers21-1 to 21-4 are formed embedded in inter-wiring insulating layers 23-1to 23-4, respectively. (Here, the inter-wiring insulating layers 23-1 to23-4 are combinations of insulating layers 25-1 to 25-4 and capinsulating layers 26-1 to 26-4, respectively.) The wiring layers 21-1 to21-4, which are formed to be adjacent to each other in an up-and-downdirection, are connected selectively by means of connection portions22-1 to 22-4, respectively. FIG. 1 shows an example in which all of thewiring layers 21-1 to 21-4 are connected in common in a region 20indicated by broken line. It should be noted here that the connectionportion 22-1 of the first wiring layer 21-1 is connected to, forexample, a drain region of the MOSFET although it is not shown in thefigure.

The wiring layers 21-1 to 21-4 and the connection portions 22-1 to 22-4are made of conductive layers 27-1 to 27-4, seed layers 28-1 to 28-4 andlower diffusion inhibiting layers 29-1 to 29-4, respectively.

The conducting layers 27-1 to 27-4 are formed embedded in theinter-wiring insulating layers 23-1 to 23-4, respectively. The seedlayers 28-1 to 28-4 are formed between the conductive layers 27-1 to27-4 and the lower diffusion inhibiting layers 29-1 and 29-4,respectively. The lower diffusion inhibiting layers 29-1 and 29-4 areformed in the boundaries with respect to the inter-wiring insulatinglayers of 23-1 to 23-4. It should be noted that the seed layers 28-1 to28-4 are integrated with the conductive layers, 27-1 to 27-4,respectively, and therefore the boundaries unclear. Thus, in many cases,there are no substantial boundaries formed.

Upper diffusion inhibiting layers 30-1 to 30-4 are formed on the capinsulating layers 26-1 to 26-4, the conductive layers 27-1 to 27-4, theseed layers 28-1 to 28-4 and the lower diffusion inhibiting layers 29-1to 29-4, respectively.

The first wiring layer (the lowermost layer) 21-1 has the narrowestwiring width and the least thickness as compared to the other wiringlayers 21-2, 21-3 and 21-4. For example, the width of the first seedlayer 28-1, which is taken along a channel direction of the MOSFET 13,is as small as about 0.1 μm.

It is preferable that the first conductive layers 27-1 and the firstseed layer 28-1 should be formed of the same basis metal, for example,copper (Cu). The first seed layer 28-1 contains a small amount ofadditive element such as magnesium (Mg). The first lower diffusioninhibiting layer 29-1 is made of, for example, a tantalum film having athickness of about 10 nm.

Note that other examples of the additive element are titanium (Ti),aluminum (Al), tin (Sn), palladium (Pb), ruthenium (Ru), rhodium (Rh),chromium (Cr), silver (Ag), cobalt (Co), indium (In), copper (Cu), etc.

The first insulating layer 25-1 should preferably be made of a materialhaving a low specific inductive capacity. In this embodiment, this layeris made of, for example, a SiOC film having a specific inductivecapacity of about 2.5. Alternatively, the first insulating layer 25-1may be made of, for example, a silicate-based film or polymer-basedfilm.

There are two types of silicate-based film, one is an organic-based filmthat contains an organic component and the other is an inorganic-basedfilm that contains no organic component. Further, in some cases, it isnot always necessary that the device should be made of a material with alow specific inductive capacity. That is, there are some product devicesthat do not require the lowering of the specific inductive capacity intheir insulating films. Therefore, in such a product group, it is alsopossible to employ silicon oxide films that have been generally used.

The first cap insulating layer 26-1 is formed of, for example, a SiO₂film, and the first upper diffusion inhibiting layer 30-1 is formed of,for example, a thin SiC film.

Next, the second wiring layer 21-2 has a wiring width that is slightlylarger than that of the first wiring layer 21-1, and a film thicknessthat is larger than that.

It is preferable that the second conductive layer 27-2 should be made ofa basis metal such as Cu. The second seed layer 28-2 should preferablymade of, for example, an almost pure basis metal of Cu that does notcontain additive element. The thickness of this layer is about 80 nm.The second lower diffusion inhibiting layer 29-2 is made of, forexample, a tantalum film having a thickness of about 15 nm.

The second insulating layer 25-2 is made of, for example, a SiOC filmhaving a specific inductive capacity of about 2.5. The second upperdiffusion inhibiting layer 30-2 is formed of, for example, a thin SiCfilm.

Next, the third wiring layer 21-3 has a wiring width that is slightlylarger than that of the second wiring layer 21-2, and a film thicknessthat is larger than that. It is preferable that the third conductivelayer 27-3 should be made of a basis metal such as Cu, and the thicknessof this layer is about 100 nm. The third seed layer 28-3 shouldpreferably made of, for example, an almost pure basis metal of Cu thatdoes not contain additive element. The third lower diffusion inhibitinglayer 29-3 is made of, for example, a tantalum nitride film having athickness of about 15 nm.

The third insulating layer 25-3 is made of, for example, afluorine-added silicon oxide film having a specific inductive capacityof about 3.0. The third upper diffusion inhibiting layer 30-3 is formedof, for example, a thin SiN film.

Next, the fourth wiring layer 21-4 is the uppermost layer, and has thelargest wiring width and largest film thickness of all the layers.

The fourth conductive layer 27-4 is made of a basis metal such as Cu,the thickness of this layer is about 1500 nm. The fourth seed layer 28-4should preferably made of, for example, an almost pure basis metal of Cuthat does not contain additive element. The fourth lower diffusioninhibiting layer 29-4 is made of, for example, a tantalum nitride filmhaving a thickness of about 30 nm.

The fourth insulating layer 25-4 is made of, for example, a siliconoxide film having a relatively large specific inductive capacity (ofabout 4.0). The fourth upper diffusion inhibiting layer 30-4 is formedof, for example, a thin SiN film.

On the fourth upper diffusion inhibiting layer 30-4, for example, asilicon nitrogen film (SiN film) is formed, thus forming an upperinsulating layer 35.

As described above, the additive element is added to each of the seedlayers 28-1 to 28-4 in such a manner that the concentration of theadditive is higher or equal in an upper layer side, and theconcentration thereof is lower in the uppermost layer than in thelowermost layer. Accordingly, the resistance values of the wiring layers21-1 to 21-4 are in such a fashion that those of the upper layer sidehave higher or equal resistance value, and the resistance value is lowerin the uppermost layer than in the lowermost layer.

Consequently, as the level of the layer is lower in the wiring layers21, the concentration of the additive element in that layer is higher,and the current density is lower. Thus, the reliability is improved moreas the layer level is lower. Especially, in the case of the lowermostwiring layer 21-1, the wiring width, in many cases, becomes as small asits minimum processing measurement. Therefore, the above-describedstructure is even more advantageous.

On the other hand, in the upper one of the wiring layers 21, an almostpure basis metal such as of Cu is applied to, for example, the seedlayers 28 and conductive layers 27. With this structure, the resistancevalue of the upper one of the wiring layers 21 becomes low, andtherefore it is possible to allow a great amount of current to flow.Especially, in the case of the uppermost wiring layer 21-4, a greatamount of current supplied from a power line or the like, can be made toflow. Therefore, the above-described structure is even moreadvantageous.

On the other hand, in the upper one of the wiring layers 21, an almostpure basis metal such as of Cu is applied to, for example, the seedlayers 28 and conductive layers 27. With this structure, the resistancevalue of the upper one of the wiring layers 21 becomes low, andtherefore it is possible to allow a great amount of current to flow.Especially, in the case of the uppermost wiring layer 21-4, a greatamount of current supplied from a power line or the like, can be made toflow. Therefore, the above-described structure is even moreadvantageous.

As described above, the concentration of the additive element in thelower one of the wiring layers, where the importance is placed speciallyon the reliability, is increased, whereas the concentration of theadditive element in the upper one of the wiring layers, where a greatamount of current should be made to flow, is lowered. In this manner,the improvement of the reliability and the lowering of the wiringresistance can be achieved both at the same time.

Further, the additive element introduced to the seed layers 28 issegregated mainly in the boundaries of the seed layers 28, morespecifically, the boundary 25 between one of the seed layers 28 and therespective one of the conductive layers 27, and the boundary between oneof the seed layers 28 and the respective one of the lower diffusioninhibiting layers 29. Therefore, in the boundaries between the seedlayers 28 and the conductive layers 27, when the conductive layers 27are made of a basis metal Cu, the additive element works to do “pinning”in the grain boundary of Cu (that is, the element is fixed by pinning tothe grain boundary of Cu), and thus the element serves to block thediffusion of Cu in the boundaries. Further, in the boundaries betweenthe seed layer 28 and the lower diffusion inhibiting layers 29, theadherence between each one of the seed layers 28 and the respective oneof the lower diffusion inhibiting layers 29 is improved, and thus theelement serves to block the diffusion in each of the boundaries. Thus,the reliability can be improved.

As described above, the additive element is contained in each of theseed layers 28-1 to 28-4 in such a manner that the concentration of theadditive is higher or equal in an upper layer side, and theconcentration thereof is lower in the uppermost layer than in thelowermost layer. In other words, the additive element is contained suchthat the concentration of the element is higher in a layer that has alonger boundary per cross sectional area in the basis metal layerserving as the respective conductive layer 27. With this structure, itis possible to improve the reliability of each of the conductive layers27, seed layers 28 and lower diffusion inhibiting layers 29, which arelocated in a lower side, and which should serve the need for a higherreliability due to their structures of thin film and narrow wiringwidth.

As described above, the device according to this embodiment can inhibitthe diffusion in the boundaries of the seed layers 28 and improve theadherence of the boundaries. Accordingly, it is possible to improve thereliability of the product device.

Further, the specific inductive capacity values of the insulating layers25-1 to 25-4 are in such a manner that the value is higher in those inthe upper section or equal, and the value of the uppermost layer ishigher than that of the lowermost layer. Therefore, the capacity islowered further as the level of the layer in the insulating layers 25becomes lower, and thus the signal delay can be suppressed.

With the above-described structure, the signal delay can be decreasedand the reliability can be improved in the multi-layer wiring section asa whole.

Further, in the upper diffusion inhibiting layers 30-1 to 30-4 as well,for example, a SiNC film, which has a lower specific inductive capacity,is employed in a lower one, and, for example, a SiN film, which has ahigher specific inductive capacity, is employed in an upper one.Therefore, due to a similar effect to that described above, the signaldelay can be further suppressed.

Furthermore, the lower diffusion inhibiting layers 29-1 to 29-4 areformed in the boundaries between the seed layers 28-1 to 28-4 and theinter-wiring insulating layers 23-1 to 23-4. With this structure, it ispossible to prevent metals and the like contained in the seed layers28-1 to 28-4 from diffusing into the inter-wiring insulating layers 23-1to 23-4.

Next, with reference to FIGS. 2 to 10, the method of manufacturing thesemiconductor device according to the first embodiment will now bedescribed by taking, as an example, the case of the four-layer wiringsemiconductor device shown in FIG. 1.

In these diagrams showing the steps of the manufacturing method with thecross sectional views of a semiconductor, the explanations of the stepsof forming the element insulating film 12 and the MOSFET 13 are omitted,and the sections directly related to the steps of forming the firstconductive layer (lowermost layer) 21-1, the second conductive layer(middle layer) 21-2, the third conductive layer (upper layer) 21-3 andthe fourth conductive layer (uppermost layer) are illustrated. Here, theexplanations will be made in connection with an example case where anembedding type Cu wiring (especially, dual-Damascene process).

First, the element insulating film 12 and the MOSFET 13 are formed by aconventional process. Then, as shown in FIG. 2, a TEOS film or the likeis deposited on the main surface of the semiconductor substrate 11 by,for example, a CVD (chemical vapor deposition) method, thereby formingthe inter-layer insulating film 17.

After that, SiOC (having a specific inductive capacity of about 2.5) isdeposited on the inter-layer insulating film 17 by, for example, a lowpressure plasma CVD method, thereby forming the first insulating layer25-1. Further, SiO₂ is deposited on the resultant by, for example, a lowpressure plasma CVD method, thereby forming the first cap layer 26-1. Itshould be noted here that the first cap insulating layer 26-1 serves asa cap film in a CMP (chemical mechanical polishing) process in a laterstep.

Here, there are several possible techniques for forming the firstinsulating layer 25-1, that is, for example, a technique of forming asilicate-based film or polymer-based film by the spin-coat method, andthe technique of forming an organic-based film by the polymerizationvapor deposition method. In the above-description, the process offorming a film having a low specific inductive capacity by the lowpressure plasma CVD method was described. However, some product devicesdo not require to lower the specific inductive capacity in aninter-layer insulating film, and therefore in such a product group, asilicon oxide film or the like, which is conventionally used and formedby the CVD method, may be employed.

Further, a photoresist 40 is coated on the entire surface of the firstcap insulating layer 26-1, and the photoresist 40 is subjected toexposure and development to pattern the photoresist.

Subsequently, as shown in FIG. 3, the first cap insulating layer 26-1and the first insulating layer 25-1 are etched anisotropically one afteranother with an RIE (reactive ion etching) method using the photoresist40 as a mask, thereby forming a wiring groove (trench) in which the fistconductive layer is embedded. After that, the photoresist 40 is removed.

Further, a basis metal, which gives rise to the first conductive layer,is applied thereon to fill cavities above the first cap insulating film26-1. In this filling process, first, a tantalum (Ta) film 39 is formedby, for example, a spattering method to have a thickness of about 10 nm.Then, on the entire surface of the tantalum film 39, a Cu film 41 isformed to have a thickness of about 80 nm by, for example, a spatteringmethod that uses a spatter target to which a small amount of magnesium(Mg) has been added. On the Cu film 41, a Cu film 42 having a thicknessof about 800 nm is formed by, for example, an electric plating method.

Subsequently, as shown in FIG., the Cu film 42 is planed by, forexample, a CMP method, so as to leave the Cu films 41 and 42 and thetantalum film 39 only in each wiring groove, and thus the firstconductive layer 27-1, the first seed layer 28-1 and the first lowerdiffusion inhibiting layer 29-1 are formed. Further, on the entiresurface, a thin SiOC film is deposited by, for example, a plasma CVDmethod, and thus the first upper diffusion inhibiting layer 30-1 isformed. Thus, the first wiring layer 21-1 is formed by theabove-described process.

It should be noted that usually, the first seed layer 28-1 and the firstconductive layer 27-1 are formed integrated as the Cu layers by theprocess in which the Cu film 42, which gives rise to the firstconductive layer 27-1, is formed by the electric plating method or thelike after forming the Cu film 41, which gives rise to the first seedlayer 28-1. Therefore, the boundary between the first seed layer 28-1and the first conductive layer 27-1 is not made prominent, and thereforein many cases, these layers are made without a substantial boundarybetween them. This is also the case for each of the boundaries betweenthe other seed layers 28-2 to 28-4 and the other conductive layers 27-2to 27-4, respectively.

Further, as shown in FIG. 4, an SiOC (having a specific inductivecapacity of about 2.5) film or the like formed by for example, a lowpressure plasma CVD method, is deposited, thereby forming the secondinsulating layer 25-2. Further, SiO2 is deposited on the secondinsulating layer resultant by, for example, a low pressure plasma CVDmethod, thereby forming the second cap insulating layer 26-2.

Subsequently, as shown in FIG. 5, a contact hole 43 having such a depththat reach the first conductive layer 27-1 is formed to pierce throughthe second insulating layer 25-2 and the second cap insulating layer26-2 by the process of a dry etching method such as photolithography orRIE similar to that shown in FIG. 3. After that, the wiring groove 44 isformed by similar steps.

Next, as shown in FIG. 6, a metal film, which is connected to the firstconductive layer 27-1 and serves as connecting metal, is applied thereonto fill cavities. In this filling process, first, a tantalum film, whichserves as a diffusion inhibiting layer for the second conductive layeris deposited in the wiring groove 44 and the contact hole 43 by, forexample, a spattering method to have a thickness of about 15 nm. Then,on the entire surface of the tantalum film, a Cu film is formed to havea thickness of about 80 nm by, for example, a spattering method thatuses a spatter target that does not contain any additive element. Inthis filling process, unlike the above-described process, a spattertarget that does not contain any additive element is used in order tosuppress the increase in the resistance that is caused by the additionalelement. After that, a Cu film having a thickness of about 800 nm isformed on the entire surface that includes the contact hole 44 and thewiring groove 43 by, for example, an electric plating method.

Further, for example, the tantalum film and Cu film are planed by, forexample, a CMP method, so as to leave the conductive layers only in eachwiring groove, and thus the second conductive layer 27-2, the secondseed layer 28-2 and the second lower diffusion inhibiting layer 29-2 areformed.

Furthermore, on the entire surface of each of the second conductivelayers 27-2 and 28-2 and the second cap insulating layer 26-2, a thinSiC film is deposited by, for example, a plasma CVD method, and thus thesecond upper diffusion inhibiting layer 30-2 is formed.

Next, a fluorine-added silicon oxide film having a slightly higherspecific inductive capacity (specific inductive capacity of about 3.0)than the above-described case, is deposited by, for example, a lowpressure plasma CVD method, on the second upper diffusion inhibitinglayer 30-2, thereby forming the third insulating layer 25-3. Then, SiO₂is deposited on the third insulating layer 25-3 by, for example, a lowpressure plasma CVD method, thus forming the cap insulating layer 26-3.

Subsequently, as shown in FIG. 7, the connecting hole 45 and the wiringgroove 46 are formed by a lithography method and dry etching methodsimilar to those mentioned above.

Next, as shown in FIG. 8, a metal film, which serves as the thirdconductive layer, is applied thereon to fill cavities. The thirdconductive layer is an upper layer, which has a wiring width and a filmthickness larger than those of the middle layer.

In this filling process, first, a tantalum nitride film, which serves asa diffusion inhibiting layer for the Cu layer, is deposited in theentire surface including the wiring groove 45 and the contact hole 46by, for example, a spattering method to have a thickness of about 20 nm.Then, on the entire surface of the tantalum nitride film which includesthe wiring groove 46 and connecting hole 45, a Cu film is formed to havea thickness of about 100 nm by, for example, a spattering method thatuses a spatter target that does not contain any additive element. Afterthat, on this Cu film, a Cu film having a thickness of 1000 nm is formedby, for example, an electric plating method.

Further, for example, the tantalum film and Cu film are planed by, forexample, a CMP method, so as to leave the conductive layers only in eachwiring groove, and thus the third conductive layer 27-3, the third seedlayer 28-3 and the third lower diffusion inhibiting layer 29-3 areformed. Then, on the entire surface of each of these layers, a thin SiNfilm is deposited by, for example, a plasma CVD method, and thus thethird upper diffusion inhibiting layer 30-3 is formed.

The fourth wiring layer 21-4 is the uppermost layer and has the largestwiring width and largest film thickness of all the layers. First, asilicon oxide film having even a higher specific inductive capacity(specific inductive capacity of about 4.0) than the above-describedcase, is deposited by, for example, a low pressure plasma CVD method, onthe entire surface, thereby forming the fourth insulating layer 25-4.

Subsequently, as shown in FIG. 9, the connecting hole and the wiringgroove are formed by lithography method and dry etching method similarto those mentioned above. Further, on the entire surface, a tantalumnitride film 47, which serves as a diffusion inhibiting layer for the Culayer is formed by, for example, a spattering method to have a thicknessof about 30 nm. Then, on the tantalum nitride film 47 including thewiring groove and connecting hole, a Cu film 48 is formed to have athickness of about 200 nm by, for example, a spattering method that usesa spatter target that does not contain any additive element. In thisfilling process, unlike the above-described process, a spatter targetthat does not contain any additive element is used in order to suppressthe increase in the resistance that is caused by the additional element.After that, a Cu film 49 having a thickness of about 1500 nm is formedon the Cu film 48 by, for example, an electric plating method.

Subsequently, as shown in FIG. 10, the tantalum nitride film 47 and theCu films 48 and 49 are planed by, for example, a CMP method, so as toleave the layers only in each wiring groove, and thus the fourthconductive layer 27-4, the fourth seed layer 28-4 and the fourth lowerdiffusion inhibiting layer 29-4 are formed. Further, on the entiresurface of each layer, a thin SiN film is deposited by, for example, aplasma CVD method, and thus the fourth upper diffusion inhibiting layer30-4 is formed. Lastly, on the entire surface, an SiN film or the likeis formed by, for example, a plasma CVD method, and thus the upperinsulating layer 35 is formed.

In the above-described process, the semiconductor device shown in FIG. 1can be manufactured.

According to the above-described manufacturing method, the concentrationof the additive element in lower layers of the seed layers 28 isincreased, and thus the resistance value of the lower layer of thewiring layers 21, where a high reliability is required, is increased todecrease the current density. In this manner, the reliability can beimproved. On the other hand, the concentration of the additive elementin upper layers of the seed layers 28 is decreased (or the additiveelement is avoided), and thereby the resistance value of upper layers ofthe wiring layers 21, which require a great amount of current to flowtherein, is decreased. In this manner, the reliability of the wiringlayers 21-1 to 21-4 can be improved.

Further, as described above, the additive element is segregated mainlyto the boundaries of the seed layers 28, and it serves to inhibit theboundary diffusion. More specifically, the boundary diffusion of,particularly, the lower layers of the wiring layers 21 is inhibited, andthe adherence of the boundaries can be improved. In this manner, thereliability can be improved.

Further, an insulating material having a low specific inductive capacityis selected and used for lower layers, to form the insulating layers 25.Therefore, the capacity of the lower ones of the insulating layers 25,which have widths smaller than those of the wiring layers 21, isdecreased, and thus the signal delay is can be reduced.

As described above, with the method according to the embodiment, it ispossible to provide a method of manufacturing a semiconductor devicethat can reduce the signal delay and improve the reliability.

In the above-described process, the technique in which the additiveelement is contained in the seed layers 28 is presented by taking anexample where the spattering method that uses a spatter targetcontaining additive element is employed. As the technique of adding theadditive element, various methods can be considered, that is, forexample, adding the element to the lower diffusion inhibiting layer 29,adding it to plating liquid, applying it on the surface of theconductive layers 27 after the plating step and diffusing it, andflattening the conductive layers 27 and then applying the additiveelement on the surface of the conductive layer 27, thereby diffusing it,etc.

Second Embodiment

Next, a semiconductor device and a method of manufacturing the device,according to the second embodiment of the present invention, will now bedescribed with reference to FIGS. 11 to 15. In the followingdescriptions, the sections that overlap with those of the firstembodiment will be omitted.

FIG. 11 is a diagram schematically showing a cross section of thesemiconductor device according to the second embodiment. As shown inFIG. 11, this embodiment is an example of a so-called hybrid structurein which the insulating layers formed in the sides of wiring portions(via portions) 21 and connecting sections 22 of the conductive layersare made of different kinds of insulating materials.

As shown in FIG. 11, wiring portion insulating layers 51-1 to 51-4 andconnecting portion insulating layers 52-1 to 52-4 are alternately formedone on another. In the wiring portion insulating layers 51-1 to 51-4,wiring layers 21-1 to 21-4 are formed to be embedded therein. In theconnecting portion insulating layers 52-1 to 52-4, connecting portions22-1 to 22-4 are formed to be embedded therein.

On the wiring portion insulating layers 51-1 to 51-4, cap insulatinglayers 26-1 to 26-4 each made of, for example, SiO₂ film, arerespectively formed. On the cap insulating layers 26-1 to 26-4, upperdiffusion inhibiting layers 30-1 to 30-4 each made of, for example, SiCfilm, are respectively formed.

As the first wiring portion insulating layer 51-1, for example, an SiO₂film having a specific inductive capacity of about 2.5 is formed.

As the second wiring portion insulating layer 51-2, for example, apolyarylene film having a specific inductive capacity of about 2.7 isformed. As the second connecting portion insulating layer 52-2, forexample, an SiOC film having a specific inductive capacity of about 2.5is formed.

As the third wiring portion insulating layer 51-3, for example, apolyarylene film having a specific inductive capacity of about 2.7 isformed. As the third connecting portion insulating layer 52-3, forexample, an SiOC film having a specific inductive capacity of about 2.5is formed.

As the fourth wiring portion insulating layer 51-4, for example, asilicon oxide film having a specific inductive capacity of about 4.0 isformed. As the fourth connecting portion insulating layer 52-4, forexample, a silicon oxide film having a specific inductive capacity ofabout 4.0 is formed. The rest of the structure is similar to that of thesemiconductor device shown in FIG. 1.

With the above-described structure, an advantageous effect similar tothat of the first embodiment can be obtained. Further, the wiringportion insulating layers 51 and the connecting portion insulatinglayers 52 are made of insulating materials having different etchingratios. Thus, the dispersion in depth is narrowed, and therefore thereliability of the device can be improved.

Next, with reference to FIGS. 12 to 15, the method of manufacturing thesemiconductor device according to the second embodiment will now bedescribed by taking, as an example, the case of the semiconductor deviceshown in FIG. 11.

In these diagrams showing the steps of the manufacturing method with thecross sectional views of a semiconductor, the explanations of the stepsof forming the element insulating film 12 and the MOSFET 13 are omitted.

First, with a technique similar to that presented in connection with thefirst embodiment, an inter-layer insulating film 17 is formed on themain surface of a semiconductor substrate 11.

Subsequently, as shown in FIG. 12, for example, an SiOC film having aspecific inductive capacity of about 2.5 is deposited by a low pressureplasma CVD method, and thus the first wiring portion insulating layer51-1. On the first wiring portion insulating layer 51-1, for example, anSiO₂ film is deposited by a low pressure plasma CVD method, and thus thecap insulating layer 26-1 is formed. Various methods can be consideredas the technique of forming the first wiring portion insulating layer51-1, as in the case of the first insulating film 25-1.

Next, as shown in FIG. 13, the first wiring layer 21-1 is formed by astep similar to that of the first embodiment. Further, on the entiresurface, for example, an SiOC film having a specific inductive capacityof about 2.5 is deposited by a low pressure plasma CVD method, and thusthe second connecting portion insulating layer 52-2. Furthermore, on theentire surface, for example, a polyarylene film having a high etchingsection ratio with respect to the second connecting portion insulatinglayer 52-2 is deposited by a coating method, and thus the second wiringinsulating layer 51-2 is formed.

Then, a hole 55 is made to pierce through the second wiring portioninsulating layer 51-2, the second connecting portion insulating layer52-2 and the first upper diffusion inhibiting layer 30-1 by process of aphotolithography or dry etching method such as RIE similar to thoseshown in FIG. 3. In this process, the second connecting portioninsulating layer 52-2 can be etched at a high etching selection ratiowith respect to the second wiring portion insulating layer 51-2. In thismanner, the dispersion in depth of the holes can be narrowed.

Subsequently, as shown in FIG. 14, the second upper diffusion inhibitinglayer 30-2 is formed by deposition, and the second conductive layer 21-2and the second connecting portion 22-2 are formed by steps similar tothose of the first embodiment. Further, on the second upper diffusioninhibiting layer 30-2, for example, an SiOC film having a specificinductive capacity of about 2.5 is deposited by a low pressure plasmaCVD method, and thus the third connecting portion insulating layer 52-3is formed. On the third connecting portion insulating layer 52-3, forexample, a polyarylene having a high etching selection ratio withrespect to the third connecting portion insulating layer 52-3 isdeposited by a coating method, and thus the third wiring portioninsulating layer 51-3 is formed.

Next, as shown in FIG. 15, the third conductive layer 21-3 and the thirdconnecting portion 22-3 are formed by steps similar to those describedabove, and the third upper diffusion inhibiting layer 30-3 is formed.Further, on the third upper diffusion inhibiting layer 30-3, forexample, a silicon oxide film having a specific inductive capacity ofabout 4.0 is deposited by a low pressure plasma CVD method, and thus thefourth connecting portion insulating layer 52-4 is formed. On the fourthconnecting portion insulating layer 52-4, for example, a polyarylenehaving a high etching selection ratio with respect to the fourth wiringportion insulating layer 52-4 is deposited by a coating method, and thusthe fourth connecting portion insulating layer 51-4 is formed.

Then, by steps similar to those of the above-described embodiment, thefourth wiring layer 21-4, the fourth connecting portion 22-4 and thefourth diffusion inhibiting layer 30-4 are formed, and thus thesemiconductor device shown in FIG. 11 can be manufactured.

As described above, the wiring layers 21 are formed to be embedded inthe wiring portion insulating layers 51, respectively, and theconnecting portions (Via portions) 22 are formed to be embedded in thewiring portion insulating portions 51, respectively. Further, the wiringportion insulating layers 51 and the connecting portion insulatinglayers 52 are formed of selected insulating materials having differentetching ratios, and therefore the wiring portion insulating layers 51can be etched at a high selection ration with respect to the connectingportion insulating layers 52. Consequently, while carrying out etchingto make holes in which conductive layers are formed, the dispersion indepth can be narrowed.

Third Embodiment

Next, a semiconductor device and a method of manufacturing the device,according to the third embodiment of the present invention, will now bedescribed with reference to FIGS. 16 to 19. FIG. 16 is a diagramschematically showing a cross section of the semiconductor deviceaccording to the third embodiment.

As shown in FIG. 16, this embodiment is described by taking, as anexample, a case where upper diffusion inhibiting layers 61-1 to 61-4 arelocated on only the conductive layers 27, the seed layers 28 and thelower diffusion inhibiting layers 29, respectively. It is preferablethat the above-mentioned diffusion inhibiting layers 61-1 to 61-4 shouldbe made of, for example, a metal such as Ta. The rest of the structureis similar to that of the first embodiment.

With the above-described structure, an advantageous effect to that ofthe first embodiment can be obtained. Further, in this embodiment,conductors are formed only on the conductive layers 27, the seed layers28 and the lower diffusion inhibiting layers 29 without employing aninsulating member having a high specific inductive capacity with respectto the inter-wiring insulating layers (cap insulating layers 26 andinsulating layers 25), as the upper diffusion inhibiting layers 61.Consequently, the increase in inter-wiring capacity, which is caused bythe upper diffusion inhibiting layers 61, can be suppressed, and thusthe signal delay can be further reduced.

Further, in the case where, for example, Cu films are used for theconductive layers 27, diffusion inhibiting layers 61 can be formed onthe Cu films respectively by using a metal such as Ta, which has a highadherence with respect to Cu. As a result, the resistance to stressmigration or the like, which is caused by boundary diffusion of Cu atom,can be improved, and thus the reliability can be further improved.

Next, with reference to FIGS. 17 to 19, the method of manufacturing thesemiconductor device according to the third embodiment will now bedescribed by taking, as an example, the case of the semiconductor deviceshown in FIG. 16. In the following descriptions, the explanations of theoverlapping sections with those of the first and second embodiments willbe omitted.

As shown in FIG. 17, first, the first wiring layer 21-1 is formed on themain surface of the semiconductor substrate 11. After that, about 10 nmof the upper portion of each of the first conductive layer 27-1, thefirst seed layer 28-1, and the first lower diffusion inhibiting layer29-1 is removed by, for example, a wet etching method.

Subsequently, as shown in FIG. 18, on the entire surface, a Ta film 65is deposited to have a thickness of 15 nm by, for example, a spatteringmethod.

Then, as shown in FIG. 19, the Ta film 65 that has been deposited isplaned by, for example, a CMP method so as to leave the Ta film 65 inthe portion removed by the etching, and thus the first upper diffusioninhibiting layer 61-1.

The above-described steps are repeated, and the other upper diffusioninhibiting layers 61-2, 61-3 and 61-4 are formed, and thus thesemiconductor device shown in FIG. 16 can be manufactured.

When forming these upper diffusion inhibiting layers 61-2 to 61-4, theupper portion of each of the conductive layers 27-2 to 27-4, the seedlayer 28-2 to 28-4, and the lower diffusion inhibiting layers 29-2 to29-4 is removed by, for example, a wet etching method. The depths of theportions removed by the etching in these layers are about 10 nm, about15 nm and about 20 nm, respectively. Further, on the entire surface, theTa films, which give raise to the upper diffusion inhibiting layers 61-2to 61-4, are deposited by, for example, a spattering method. Thethicknesses of these layers are about 15 nm, about 20 nm and about 25nm, respectively.

Further, in the first to third embodiment, the addition of the elementto the basis metal is carried out by use of the spattering target of thealloy. Here, it is alternatively possible that the element is added inthe following manner. That is, the layer is deposited by using a coppertarget that does not contain any additive element, and then the additiveelement is deposited, followed by a heat treatment. It is furtheralternatively possible that the element is added by means of a techniquesuch as ion implantation.

It should be noted here that, naturally, the number of wiring layers isnot limited to four as long as it is two or more.

Further, the above-described embodiments were described in connectionwith only the case where the copper (cu) film is used as an example ofthe basis metal; however it is alternatively possible that theconductive layers are formed by using some other basis metal thancopper, that is, for example, using silver or the like as the basismetal.

Further, the above-described embodiments were described in connectionwith the case where there is only one component in the additive element;however it is alternatively possible that there are two or morecomponents. Also, not only the element used to improve the reliabilityof the wiring layers, is contained, but also an additive element thatcan secure a adhesion, for example, can be contained. Apart from these,the present invention can be remodeled into various versions as long asthe essence of the invention does not fall out of the scope of theinvention.

As described in detail, according to the embodiments of the presentinvention, the additive element is supplied to at least one layer of abasis metal, for the conductive layers that constitute the multi-layerwiring portion. With this structure, the additive element can besupplied to the basis metal of the thin film layer located at thelowermost section, that has the minimum processible measurements. Thus,the current density of the wiring layers can be lowered, and thediffusion at the boundaries between the wiring layers can be suppressed.In this manner, the reliability of the wiring can be improved.Consequently, it is possible to achieve multi-layer wiring that canimprove the wiring reliability even with a thin film.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor device comprising: a semiconductor substrate; amulti-layer wiring portion including insulating layers and wiring layersalternately stacked one on another on a main surface of thesemiconductor substrate, all of the wiring layers being made of a samebasis metal, at least one of the wiring layers containing an additiveelement, and a concentration of the additive element being lower on anupper layer side than that on a lower layer side, the upper and lowerlayer sides are that of the multi-layer wiring portion; and upperdiffusion inhibiting layers formed on the top of the wiring layers, afilm thickness of an upper diffusion inhibiting layer on an upper sideof an adjacent pair of the upper diffusion inhibiting layers is thickerthan or equal to that of an upper diffusion inhibiting layer located ona lower side of the adjacent pair, wherein a specific inductive capacityof an insulating layer located on an upper side of an adjacent pair ofinsulating layers included in the multi-layer wiring portion is equal toor higher than that of an insulating layer located on a lower side ofthe adjacent pair, and the specific inductive capacity of the lowermostlayer is lower than that of the uppermost layer.
 2. The semiconductordevice according to claim 1, wherein the concentration of the additiveelement is lower as a length of a boundary per cross sectional area islarger in the basis metal.
 3. The semiconductor device according toclaim 2, wherein the basis metal contains at least one of copper,aluminum and silver.
 4. The semiconductor device according to claim 1,wherein each of the wiring layers is embedded in a wiring groove of arespective one of the insulating layers.
 5. The semiconductor deviceaccording to claim 1, wherein the basis metal contains at least one ofcopper, aluminum and silver.
 6. The semiconductor device according toclaim 1, wherein the additive element comprises at least one of Mg, Ti,Al, Sn, Pb, Ru, Rh, Cr, Ag, Co, In and Cu.
 7. The semiconductor deviceaccording to claim 1, wherein a current density of the wiring layers isdecreased in inverse proportion to the concentration of the additiveelement.
 8. The semiconductor device according to claim 1, wherein theconcentration of the additive clement of an inner section of the basismetal is lower than or equal to that of a section close to a surface ofthe basis metal.
 9. The semiconductor device according to claim 1,further comprising: an insulating gate-type electric field effecttransistor provided in the semiconductor substrate and connectedselectively to the wiring layers within the multi-layer wiring portion.10. The semiconductor device according to claim 1, a concentration ofthe additive element is lower in an uppermost layer than in a lowermostlayer.
 11. The semiconductor device according to claim 1, wherein: eachof said wiring layers comprises a plurality of layers; a lowermost oneof said wiring layers has a first layer containing said additiveelement; and a wiring layer, disposed above said lowermost one layer,has a second layer corresponding to said first layer having aconcentration of said additive element lower than a concentration insaid first layer.
 12. A semiconductor device comprising: a semiconductorsubstrate; a plurality of insulating layers stacked upon each otherformed on said substrate, a specific inductive capacity of an insulatinglayer located on an upper side of an adjacent pair of insulating layersincluded in a multi-layer wiring portion being equal to or higher thanthat of an insulating layer located on a lower side of the adjacentpair, and the specific inductive capacity of the lowermost layer islower than that of the uppermost layer; a wiring layer formed in each ofsaid insulating layers; each of said wiring layers comprising a lowerlayer and a main conductor layer formed on said lower layer, each ofsaid lower layers being formed of the same basis metal; and upperdiffusion inhibiting layers being formed on the top of the wiringlayers, a film thickness of an upper diffusion inhibiting layer on anupper side of an adjacent pair of the upper diffusion inhibiting layersis thicker than or equal to that of an upper diffusion inhibiting layerlocated on a lower side of the adjacent pair.
 13. The semiconductordevice according to claim 12, wherein a film thickness of the uppermostdiffusion inhibiting layer is thicker than that of the lowermostdiffusion inhibiting layer.
 14. The semiconductor device according toclaim 12, wherein a width of the upper wiring layer is wider than orequal to that of the lower wiring layer.
 15. The semiconductor deviceaccording to claim 14, wherein a width of the uppermost wiring layer iswider than that of the lowermost wiring layer.
 16. The semiconductordevice according to claim 12, wherein a film thickness of the upperwiring layer is wider than or equal to that of the lower wiring layer.17. The semiconductor device according to claim 16, wherein a filmthickness of the uppermost wiring layer is wider than that of thelowermost wiring layer.
 18. The semiconductor device according to claim12, wherein a specific inductive capacity of the upper insulating layeris higher than or equal to that of the lower insulating layer.
 19. Thesemiconductor device according to claim 18, wherein a specific inductivecapacity of the uppermost insulating layer is higher than that of thelowermost insulating layer.
 20. A semiconductor device comprising: asemiconductor substrate; a multi-layer wiring portion includinginsulating layers and wiring layers alternately stacked one on anotheron a main surface of the semiconductor substrate, all of the wiringlayers being made of a same basis metal, at least one of the wiringlayers containing an additive element, and a concentration of theadditive element being lower on an upper layer side than that on a lowerlayer side, the upper and lower layer sides are that of the multi-layerwiring portion; and upper diffusion inhibiting layers formed on the topof the wiring layers, a film thickness of an upper diffusion inhibitinglayer on an upper side of an adjacent pair of the upper diffusioninhibiting layers is thicker than or equal to that of an upper diffusioninhibiting layer located on a lower side of the adjacent pair, wherein aspecific inductive capacity of an insulating layer located on an upperside of an adjacent pair of insulating layers included in themulti-layer wiring portion is equal to or higher than that of aninsulating layer located on a lower side of the adjacent pair, and thespecific inductive capacity of the lowermost layer is lower than that ofthe uppermost layer.